Airfoil for a turbine system

ABSTRACT

An airfoil includes a main portion formed of a base material. Also included is a trailing edge region of the main portion. Further included is a trailing edge supplement structure comprising at least one pre-sintered preform (PSP) material operatively coupled to the base material proximate the trailing edge region.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to airfoils, and more particularly to a trailing edge supplement structure for airfoils, particularly those in turbine systems.

Airfoils employed in various turbine systems are formed as buckets and nozzles. A working fluid such as hot gas or steam is typically forced across the airfoils, with the buckets coupled to a rotor of the turbine system. The force of the working fluid on the buckets causes the buckets, and therefore the coupled body of the rotor to rotate. As such, aerodynamic geometry of the airfoils impacts the overall system performance of the turbine system. Various manufacturing processes, such as casting, may be employed to form the airfoils, but such processes are limiting in certain respects, with one limitation relating to the aerodynamic characteristics of the manufactured airfoils.

The airfoils are typically formed of nickel, cobalt or iron-based superalloys with desirable mechanical and environmental properties for withstanding turbine operating temperatures and conditions. Because the efficiency of a turbine system is dependent on its operating temperatures, there is a demand for the airfoils to be capable of withstanding increasingly higher temperatures. As the maximum local temperature of a superalloy component approaches the melting temperature of the superalloy, forced air cooling becomes necessary. For this reason, airfoils of gas turbine buckets and nozzles often require complex cooling schemes in which steam or air, typically bleed air, is forced through internal cooling passages within the airfoil and then discharged through cooling holes at the airfoil surface to transfer heat from the component. As noted above, the processes used to manufacture airfoils is somewhat limiting and this impacts the cooling passage precision, with respect to both location and dimension.

BRIEF DESCRIPTION OF THE INVENTION

According to one aspect of the invention, an airfoil includes a main portion formed of a base material. Also included is a trailing edge region of the main portion. Further included is a trailing edge supplement structure comprising at least one pre-sintered preform (PSP) material operatively coupled to the base material proximate the trailing edge region.

According to another aspect of the invention, a turbine system includes an airfoil. Also included is a main portion of the airfoil extending from a leading edge to a trailing edge region and formed of a base material. Further included is a trailing edge supplement structure comprising a first PSP material and a second PSP material, the first PSP material and the second PSP material joined to the base material of the main portion proximate the trailing edge region. Yet further included is at least one cooling passage within the trailing edge supplement structure.

According to yet another aspect of the invention, a method of repairing a trailing edge region of an airfoil is provided. The method includes removing material proximate the trailing edge region of the airfoil. The method also includes exposing a base material of the trailing edge region. The method further includes joining at least one PSP material to the base material. The method yet further includes forming a trailing edge supplement structure upon joining of the at least one PSP material to the base material.

These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic illustration of a turbine system;

FIG. 2 is a top plan view of an airfoil;

FIG. 3 is a cross-sectional view of a trailing edge region of the airfoil;

FIG. 4 is a perspective view of a trailing edge supplement structure; and

FIG. 5 is a flow diagram illustrating a method of repairing the trailing edge region of the airfoil.

The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a turbine system 10 constructed in accordance with an exemplary embodiment of the invention, is schematically illustrated. The turbine system 10 illustrated comprises a gas turbine engine, but it is to be appreciated that embodiments described herein may be employed in alternative systems, such as a steam turbine, for example. For purposes of illustration and discussion, the gas turbine engine is referenced.

The gas turbine engine 10 includes a compressor section 12 and a plurality of combustor assemblies arranged in a can annular array, one of which is indicated at 14 and includes a combustion section 18. It should be appreciated that this invention is independent of the details of the combustion system, and the can annular system is referenced for purposes of discussion. Fuel and compressed air are passed into the combustion section 18 and ignited to form a high temperature, high pressure combustion product or air stream that is used to drive a turbine section 24. The turbine section 24 includes a plurality of stages 26-28 that are operationally connected to the compressor section 12 through a rotor 30. In particular, each of the plurality of stages 26-28 includes a nozzle 32 and a bucket 34, with the bucket 34 operatively coupled to the rotor 30. The nozzle 32 and the bucket 34 of each of the plurality of stages 26-28 are airfoils that that working fluid (e.g., air-fuel mixture) passes over. Although three stages are identified, one can appreciate that more or less stages may be present.

Referring now to FIG. 2, an airfoil 36 representing either the nozzle 32 or the bucket 34 is illustrated in greater detail. The airfoil 36 includes a main portion 38 that extends from a leading edge 40 to a trailing edge region 42. The main portion 38 is formed of a base material that may vary depending on the particular application. In some embodiments, the base material comprises a nickel-, cobalt-, or iron-based superalloy. The main portion 38 may be formed as an equiaxed, directionally solidified (DS), or single crystal (SX) casting to withstand the high temperatures and stresses to which it is subjected, such as within a gas turbine engine, for example. The trailing edge region 42 is relatively rounded and includes a trailing edge region aft width 44.

The airfoil 36 also includes a trailing edge supplement structure 46 that is operatively coupled to the main portion 38 proximate a surface of the trailing edge region 42. As shown, relative to the main portion 38, the trailing edge supplement structure 46 tapers to a thinner, more acute end portion, the dimension referred to herein as a trailing edge supplement structure aft width 48.

Referring to FIGS. 3 and 4, the trailing edge region 42 of the main portion 38 and the trailing edge supplement structure 46 are illustrated in greater detail. In the illustrated embodiment, the trailing edge supplement structure 46 includes a first PSP material, referred to herein as a PSP sheet 50 and a second PSP material, referred to herein as a PSP sheet 52 that are each pre-sintered preform (PSP) structures. The PSP sheets, namely the first PSP sheet 50 and the second PSP sheet 52, each comprise a mixture of particles comprising a first alloy and a second alloy that have been sintered together at a temperature below their melting points to form an agglomerate and somewhat porous mass. Suitable particle size ranges for the powder particles include 150 mesh, or even 325 mesh or smaller to promote rapid sintering of the particles and reduce porosity in the PSP sheets to about 10 volume percent or less.

The first alloy of the first PSP sheet 50 and the second PSP sheet 52 comprises any composition such as one similar to the base material of the main portion 38 to promote common physical properties between the PSP sheets and the main portion 38. For example, in some embodiments, the first alloy and the base material share a common composition (i.e., they are the same type of material). In some embodiments, the first alloy comprises a nickel-based superalloy or a cobalt-based superalloy. In some embodiments, the properties for the first alloy include chemical and metallurgical compatibility with the base material, such as high fatigue strength, low tendency for cracking, oxidation resistance and/or machinability.

The second alloy may also have a composition similar to the base material of the main portion 38, but further contains a melting point depressant to promote sintering of the first alloy and the second alloy particles and enable bonding of the PSP sheets to the trailing edge region 42 of the main portion 38 at temperatures below the melting point of the base material. For example, in some embodiments the melting point depressant comprises boron and/or silicon.

The PSP sheets comprise any relative amounts of the first alloy and the second alloy that are sufficient to provide enough melting point depressant to ensure wetting and bonding (e.g., diffusion/brazing bonding) of the particles of the first alloy and the second alloy to each other and to the trailing edge region 42 of the main portion 38 of the airfoil 36. For example, in some embodiments the second alloy comprises at least about 10 weight percent of each of the first PSP sheet 50 and the second PSP sheet 52. In one embodiment, the second alloy comprises about 70 weight percent of each of the PSP sheets, with the first alloy comprising about 30 weight percent of each of the PSP sheets, thereby resulting in a mixed weight ratio of the first alloy to the second alloy of about 30:70. In another embodiment, a mixed weight ratio of the first alloy to the second alloy of about 40:60 is employed.

The above-described embodiments of the trailing edge supplement structure 46 are illustrated and described as having two PSP sheets. However, it is to be understood that a single PSP sheet may be employed and operatively coupled to the trailing edge region 42 of the main portion 38. Furthermore, more than two PSP sheets may be employed to form the trailing edge supplement structure 46.

Irrespective of the precise number of PSP sheets employed, the sheet(s) are operatively coupled to the trailing edge region 42 of the main portion 38. In one embodiment, the PSP sheets are brazed to the trailing edge region 42. The PSP sheets are formed of materials configured to be brazed to the trailing edge region 42 without the need for application of a braze paste. In this way, the PSP sheets, such as the first PSP sheet 50 and the second PSP sheet 52, are positioned in a desirable location in an abutting manner with the trailing edge region 42 within a furnace and heated to a necessary temperature to facilitate brazing of the PSP sheets to the main portion 38. In addition to brazing, it is contemplated that alternative coupling techniques may be employed, including, but not limited to, welding, diffusion bonding or mechanical fastening.

Formation of the PSP sheets as the trailing edge supplement structure 46 enables thinner trailing edge portions of the airfoil 36, which effectively reduces aerodynamic blockage, thereby improving overall turbine system performance.

To provide effective cooling of the airfoil 36, a cooling arrangement 54 is implemented within the trailing edge region 42 of the main portion 38 and throughout the trailing edge supplement structure 46. The trailing edge region 42 of the main portion 38 includes at least one cooling channel 56 that is in fluid communication with at least one, but typically a plurality of cooling passages 58 disposed in the trailing edge supplement structure 46. The plurality of cooling passages 58 may be formed in a variety of manners and at a variety of times throughout the manufacturing process. Specifically, the plurality of cooling passages 58 may be formed prior to coupling of the trailing edge supplement structure 46 to the main portion 38 or subsequent to coupling.

Formation of the plurality of cooling passages 58 prior to coupling of the trailing edge supplement structure 46 to the main portion 38 may include formation of negative grooves, slots or the like into at least one of the PSP sheets during formation of the PSP sheets themselves, such that the PSP sheets are still in their pliable green state before initial sintering. The grooves, slots or the like may be formed in both of the first PSP sheet 50 and the second PSP sheet 52, such that alignment of the grooves, slots, etc. is necessary to form the plurality of cooling passages 58. Alternatively, the plurality of cooling passages 58 may be machined (i.e., removal of some material from the PSP sheet(s)) via any suitable material removal operation, including, but not limited to, milling, grinding, wire electrical discharge machining (EDM), milled EDM, plunge EDM, electro-chemical machining (ECM), water-jet trenching, laser trenching, or combinations thereof. It is contemplated that the material removal process may occur prior to coupling of the trailing edge supplement structure 46 to the main portion or after such coupling. Regardless of the time of formation of the plurality of cooling passages 58, the plurality of cooling passages 58 are in fluid communication with the at least one cooling channel 56. It is contemplated that the above-described embodiments may be incorporated into new or existing airfoils of various turbine systems.

As illustrated in the flow diagram of FIG. 5, and with reference to FIGS. 1-4, a method of repairing a trailing edge region of an airfoil 100 is also provided. The turbine system 10 and the trailing edge supplement structure 46 of the airfoil 36 have all been previously described and specific structural components need not be described in further detail. The method of repairing a trailing edge region of an airfoil 100 includes removing material proximate the trailing edge region of the airfoil 102. A base material of the trailing edge region is exposed 104 and at least one PSP sheet is joined to the base material 106. A trailing edge supplement structure is formed upon joining of the at least one PSP sheet to the base material 108. The method of repairing a trailing edge region of an airfoil 100 also includes forming at least one cooling passage that is in fluid communication with the at least one cooling channel 56 of the main portion 38, as described in detail above.

While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims. 

1. An airfoil comprising: a main portion formed of a base material; a trailing edge region of the main portion; and a trailing edge supplement structure comprising at least one pre-sintered preform (PSP) material operatively coupled to the base material proximate the trailing edge.
 2. The airfoil of claim 1, wherein the trailing edge supplement structure is brazed to the trailing edge region.
 3. The airfoil of claim 1, further comprising at least one cooling channel formed in the base material of the main portion.
 4. The airfoil of claim 3, further comprising at least one cooling passage formed in the trailing edge supplement structure, the at least one cooling passage in fluid communication with the at least one cooling channel.
 5. The airfoil of claim 1, further comprising a trailing edge supplement structure aft width and a trailing edge region aft width, wherein the trailing edge supplement structure aft width is less than the trailing edge region aft width.
 6. The airfoil of claim 1, wherein the at least one PSP material comprises a first alloy and a second alloy.
 7. The airfoil of claim 6, wherein the first alloy and the second alloy are mixed together at a weight ratio of about 30:70.
 8. The airfoil of claim 1, wherein the at least one PSP material comprises a first PSP material and a second PSP material operatively coupled together.
 9. The airfoil of claim 8, wherein at least one of the first PSP material and the second PSP material includes a slot, wherein operative coupling of the first PSP material and the second PSP material forms at least one cooling passage.
 10. The airfoil of claim 9, wherein the at least one cooling passage is in fluid communication with at least one cooling channel formed in the base material of the main portion.
 11. A turbine system comprising: an airfoil; a main portion of the airfoil extending from a leading edge to a trailing edge and formed of a base material; a trailing edge supplement structure comprising a first PSP material and a second PSP material, the first PSP material and the second PSP material joined to the base material of the main portion proximate the trailing edge; and at least one cooling passage within the trailing edge supplement structure.
 12. The turbine system of claim 11, wherein at least one of the first PSP material and the second PSP material includes a slot, wherein operative coupling of the first PSP material and the second PSP material forms the at least one cooling passage.
 13. The turbine system of claim 11, wherein the at least one cooling passage is in fluid communication with at least one cooling channel formed in the base material of the main portion.
 14. The turbine system of claim 11, further comprising a trailing edge supplement structure aft width and a trailing edge region aft width, wherein the trailing edge supplement structure aft width is less than the trailing edge region aft width.
 15. The turbine system of claim 11, wherein each of the first PSP material and the second PSP material comprises a first alloy and a second alloy.
 16. The turbine system of claim 15, wherein the first alloy and the second alloy are mixed together at a weight ratio of about 30:70.
 17. A method of repairing a trailing edge region of an airfoil comprising: removing material proximate the trailing edge region of the airfoil; exposing a base material of the trailing edge region; joining at least one PSP material to the base material; and forming a trailing edge supplement structure upon joining of the at least one PSP material to the base material.
 18. The method of claim 17, further comprising forming at least one cooling passage within the at least one PSP material prior to joining the at least one PSP material to the base material.
 19. The method of claim 17, further comprising forming at least one cooling passage within the at least one PSP material after joining the at least one PSP material to the base material.
 20. The method of claim 17, wherein the trailing edge supplement structure comprises a first PSP material and a second PSP material, the method further comprising forming at least one cooling passage within the trailing edge supplement structure by aligning a first slot of the first PSP material and a second slot of the second PSP material. 